Enables the voice search in the app-list without showing start page.

This CL instead introduces --enable-app-list-voice-search flag
and let the start page web contents loaded with that flag, but
not shown the start page in the app-list.

BUG=333914
R=xiyuan@chromium.org
TBR=derat@chromium.org
TEST=manually

Review URL: https://codereview.chromium.org/133863005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244930 0039d316-1c4b-4281-b951-d872f2087c98
Support nested tracing in gpu_tracer.

gpu_tracer used to support only one trace at a time per-context.
This change enables nested traces, which will make them more useful for
marking various groups of rendering code in the Renderer.

Multiple sources are handled. Possible sources:

  kTraceGroupMarker -> Added by glPush/PopGroupMarkerEXT()
  kTraceCHROMIUM -> Added by glTraceBegin/EndCHROMIUM()
  kTraceDecoder -> Added automatically for some commands by GLES2Decoder

The sources are separated so that they don't corrupt eachother's stack.

i.e. this is OK:

  glPushGroupMarker()
  glTraceBeginChromium()
  glPopGroupMarker()
  glTraceEndChromium()

GPU Service side trace is now enabled by category "gpu.service"
GPU Device side trace is now enabled by category "gpu.device"

BUG=331161

Review URL: https://codereview.chromium.org/134163003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244931 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244931